The invention relates to a lockable freewheeling device, and more particularly for connecting the drive of the wheels of the axle not permanently driven to the drive of the wheels of the permanently driven axle of a motor vehicle. The freewheeling device includes two freewheeling components one of which is driven with the other one being intended to pass on the rotational movement and which two components are non-rotatingly connected to one another via a switching device operated especially by a centrifugal force, up to a predetermined speed for both possible directions of rotation and, for any speeds in excess of said predetermined speed, only for a main driving direction of rotation.
A drive assembly for a four-wheel drive motor vehicle with a viscous coupling, which, via a freewheeling device, is connected to the input and for the wheels not driven permanently or is disconnected therefrom is described in U.S. Pat. No. 4,889,353. Described in that reference are two freewheeling units with clamping members, which units engage up to a predetermined speed, thus producing a non-rotating connection for both directions of rotation. From a certain speed upwards, the clamping members of the freewheeling unit which serve to transmit torque during reversing are made inoperative. This ensures that in case the rear wheels rotate faster than the front wheels, for example during braking, overtaking becomes possible. This ensures that no braking torque is transmitted by the front wheels to the rear wheels and that, even if the front wheels are overbraked, the lateral stability of the vehicle is maintained. This also ensures that at high speeds, the lateral stability of the vehicle is maintained.
However, a disadvantage of this design is that the clamping members are used directly as centrifugal weights for the movement into the open position. This means that at the slightest twisting moment (e.g. through worn rear tires), an accurate transfer into the free position is not possible.
Viscous couplings for connecting the motor vehicle wheels not driven permanently are known. Great Britain Patent Number 1,357,106 describes a system wherein the viscous coupling is arranged between the front wheels and rear wheels. The viscous coupling reacts to a speed differential between the front wheels and rear wheels. This reference also shows viscous couplings as so-called torque splitters, in which case they replace the rear wheel differential of the axle of a four-wheel drive vehicle not driven permanently. Such an assembly is known from DE 37 08 193 A1 for example. This publication also describes freewheeling units which, during driving, permanently have a locking effect in both directions of rotation, but which are released when the vehicle brake is actuated.
It is an object of the invention to provide a freewheeling device which is suitable for securely transmitting the torque in the main torque transmitting direction and which, above a certain speed level, ensures accurate disconnection when the torque operating direction is reversed while permitting the transmission of torque in both directions of rotation at low speeds, independently of the torque operating direction.
In accordance with the invention, a freewheeling device is described wherein one of the freewheeling components comprises a sleeve-shaped portion with circumferentially distributed apertures holding locking members in a radially diplaceable way. The other freewheeling component is provided with recesses circumferentially distributed so as to correspond to the recesses. The apertures and recesses comprise opposed supporting faces for the main torque transmitting direction on the one hand and for an opposite torque operating direction on the other hand. The supporting faces for the main torque transmitting direction are arranged in such a way that the normal lines relative to the contact faces, in the contact points with the locking members designed as rolling members, which extend through the center of the locking members, form a maximum angle of 185.degree. directed towards the rotational axis of the freewheeling components. The supporting faces for the opposite torque operating direction are arranged in such a way that the normal lines in the contact points with the locking members form a maximum angle of 180.degree. facing away from the rotational axis. In the sleeve-shaped portion there is provided a switching element which is axially displaceable, which, by a spring, is pushed into a position in which the locking members are held so as to be prevented from escaping in the direction of the rotational axis and which, as a function of the speed, may be moved into a releasing position via a switching device.
An advantage of this design is that if, at higher speeds, e.g. in excess of a forward speed of 25-40 km per hour depending on the type of vehicle, a transfer into the freewheeling function takes place when the torque operating direction is reversed.
Below the limit speed, the switching element ensures secure support so that during reversing, which, with respect to the torque operating direction, takes place in the direction opposite to the main torque transmitting direction, the locking members are securely supported so the four-wheel drive also functions during reversing.
According to a further embodiment of the invention, in the main torque transmitting direction, when a predetermined speed is exceeded, the locking members are held entirely by the inertia forces acting on them.
In a preferred embodiment, the supporting face for the main torque transmitting direction, with reference to the apertures, is formed by a conical face of a conical bore whose vertex is arranged on the radial inside of the sleeve-shaped portion towards the rotational axis.
According to an alternate embodiment, the axis of the conical bore extends radially relative to the rotational axis.
Alternatively, in the alternate embodiment, the axis of the conical bore is inclined and--if viewed in section--intersects the rotational axis, the distance between the axis and the rotational axis being predetermined.
For the alternate embodiment, the angle formed by the supporting face of the recess for the main torque transmitting direction with the bore axis of the conical bore may be smaller than that formed by the supporting face with the bore axis for the opposite torque operating direction.
A supporting element for tho locking members should be axially movably guided in the sleeve-shaped portion of the associated freewheeling component. For securing the position of the switching element, there should be provided securing balls which are pushed into a securing recess by the supporting element and which axially hold the switching element. The supporting faces are designed so as to be tapered towards the closing direction of the switching element.
The additional supporting element, together with the securing balls, serves to reduce the actuating force required for transferring the locking members into the freewheeling position when the driveline is twisted.
In a further embodiment, the switching element is also designed as a sleeve and the freewheeling component comprising the apertures comprises a hollow projection for providing a non-rotating connection with the journal.
Preferably, at least one of the two freewheeling components is designed as a connecting part of a joint or a shaft, as a result of which integration into the driveline is facilitated.
The freewheeling device is particularly advantageous if it cooperates with one or a plurality of viscous couplings, with the viscous coupling and freewheeling device being connected in series.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.